The present invention relates to minimizing acoustic echo effects, and more particularly to minimizing acoustic echo effects in a microphone boot. Even more particularly, the present invention relates to minimizing acoustic echo effects in a noise canceling microphone boot for a portable radio, such as a portable cellular telephone.
A major challenge faced by the designer of portable radios, such as portable cellular telephones is posed by what is known as "acoustic echo effect". This effect occurs when sound emitted from a speaker in a portable radio is transmitted to and received by a microphone in the same portable radio. For example, when a first person is talking to a second person, as the first person's voice is emitted from the speaker in the second person's portable radio, it may be picked up by a microphone in the second person's portable radio, and consequently, transmitted back to the first person. Absent any mechanism for minimizing or preventing "acoustic echo effect", the results of this transmission back to the first person is that the first person's voice is emitted from the speaker of the first person's portable radio, thus "echoing" the first person's own voice transmissions.
Acoustic echo effect is problematic in portable radios, such as portable cellular telephones, because of their small size and thus short distance between the microphone and speaker, and is particularly problematic in digital portable radios, such as digital cellular telephones (e.g., TDMA, CDMA, GSN and the like), and even more problematic in satellite transceivers, because of the greater delays present in digital and satellite environments. Although it is inevitable that some sound emitted from a speaker in a portable radio will be picked up by a microphone in the same portable radio, acoustic echo effect can be minimized through an effective seal around the microphone within such portable radio's housing. This seal serves to minimize the amount of sound entering the microphone from within the portable radio's housing, which accounts for the majority of acoustic echo effect. As a result, most portable radios employ a "boot" made from rubber-like material that encloses its microphone and provides a seal against plastic housings of the portable radio so as to prevent sound from entering the microphone from within the plastic housings.
Boot designs commonly employed tradeoff performance (i.e., effectivity of the seal formed around the microphone) for manufacturablity (i.e., ease and speed of assembly), or vice versa. The primary reason for this tradeoff is that the microphone typically requires two leads (either in the form of wires or a thin plastic flex conductor in which a pair of conductors are encompassed or on which such conductors are fused) in order to connect the microphone with a circuit board within the plastic housings. As a result, there is generally a compromise in the integrity of the seal at the point or points from which these two leads emerge from the boot. If the point or points at which the leads emerge is sealed well, then assembly becomes highly difficult, because the leads must be squeezed through tight openings in the microphone's boot. On the other hand, if the point or points at which the leads emerge is not sealed well, then assembly is simplified, but acoustic echo may be worsened because sound is able to enter the microphone through these points.
The present invention advantageously addresses the above and other needs.